Backside Polisher with Dry Frontside Design and Method Using the Same

ABSTRACT

The present disclosure provides a semiconductor fabrication apparatus in accordance with one embodiment. The apparatus includes a wafer stage that is operable to secure and rotate a wafer; a polish head configured to polish a backside surface of the wafer; an air bearing module configured to apply an air pressure to a front surface of the wafer; and an edge sealing unit configured to seal edges of the wafer.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experiencedexponential growth. Technological advances in IC materials and designhave produced generations of ICs where each generation has smaller andmore complex circuits than the previous generation. In the course of ICevolution, functional density (i.e., the number of interconnecteddevices per chip area) has generally increased while geometry size(i.e., the smallest component or line that can be created using afabrication process) has decreased. This scaling down process generallyprovides benefits by increasing production efficiency and loweringassociated costs. Such scaling down has also increased the complexity ofprocessing and manufacturing ICs and, for these advances to be realized,similar developments in IC processing and manufacturing are needed. Inone example, polishing is applied to semiconductor wafer. However, theexisting polish systems and the corresponding methods are not effectiveand may introduce additional issues, such as contaminations and damagesto the wafer. Accordingly, it would be desirable to provide a polishsystem and a method of utilizing thereof absent the disadvantagesdiscussed above.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussions.

FIG. 1 is a schematic and sectional view of a polish module constructedin accordance with some embodiments.

FIG. 2 is a schematic view of an edge sealing unit of the polish modulein FIG. 1, constructed in accordance with some embodiments.

FIG. 3 is a schematic view of an edge sealing unit of the polish modulein FIG. 1, constructed in accordance with some embodiments.

FIG. 4 is a schematic and sectional view of the polish module of FIG. 1,in portion, constructed in accordance with some embodiments.

FIG. 5A is a schematic and sectional view of a polish module, inportion, constructed in accordance with some embodiments.

FIG. 5B is a schematic and sectional view of a polish module, inportion, constructed in accordance with some embodiments.

FIG. 6 is a schematic and sectional view of a polish module, in portion,constructed in accordance with some embodiments.

FIG. 7A is a schematic and sectional view of a polish module, inportion, constructed in accordance with some embodiments.

FIG. 7B is a schematic and sectional view of a polish module, inportion, constructed in accordance with some embodiments.

FIG. 8 is a block diagram of a polish system having a polish module ofFIG. 1, constructed in accordance with some embodiments.

FIG. 9 is a flowchart of a method utilizing the polish system of FIG. 8,constructed in accordance with some embodiments.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof various embodiments. Specific examples of components and arrangementsare described below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. For example, if the device in the figures is turned over,elements described as being “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the exemplary term “below” can encompass both an orientation ofabove and below. The apparatus may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein may likewise be interpreted accordingly.

FIG. 1 illustrates a schematic and sectional view of a polish module 100in accordance with some embodiments. The polish module 100 includes asubstrate stage 102 designed to secure a semiconductor wafer 104 andhaving a mechanism to rotate the wafer 104 around an axis 106, which isperpendicular to the wafer 104 and passes its center. For examples, thesubstrate stage 102 may include clamping structure to secure the edgesof the semiconductor wafer 104. In other examples, the substrate stage102 further includes a rotation structure and a motor integrated toenable the rotation of the semiconductor wafer 104.

In some embodiments, the semiconductor wafer 104 is a silicon wafer. Insome embodiments, the semiconductor wafer 104 may include an elementarysemiconductor, such as germanium in a crystalline structure; a compoundsemiconductor, such as silicon germanium, silicon carbide, galliumarsenic, gallium phosphide, indium phosphide, indium arsenide, and/orindium antimonide; or combinations thereof. In furtherance of theembodiments, those semiconductor material films may be epitaxially grownon the silicon wafer. In some other embodiments, the wafer 104 may be asubstrate of other material.

The semiconductor wafer 104 has a front surface 104A and a backsidesurface 104B opposing from each other. One or more integrated circuitsare formed, partially formed or to-be formed on the front surface 104Aof the semiconductor wafer 104. Therefore, the front surface 104A of thesemiconductor wafer 104 includes a patterned material layer or amaterial layer to be patterned. For examples, the front surface 104A mayinclude various isolation features (such as shallow trench isolationfeatures), various doped features (such as doped wells, or doped sourceand drain features), various devices (such as transistors), variousconductive features (such as contacts, metal lines and/or vias of aninterconnection structure), packaging material layers (such as bondingpads and/or a passivation layer), or a combination thereof. On acompletely fabricated semiconductor wafer, all above material layers andpatterns may present on the front surface 104A of the semiconductorwafer 104. In the present example, the semiconductor wafer 104 is stillin the fabrication, a subset of the above material layers may be formedon the front surface 104A.

The polish module 100 includes a polish head 110 configured to polishthe backside surface 104B of the semiconductor wafer 104. The polishhead 110 includes a polish surface 112, such as an abrasive tape orother suitable polish surface. The polish surface may further includeother structure, such as a roll that is operable to roll on the waferand clean the wafer accordingly.

The polish module 100 further includes a mechanism 114 that is operableto apply a pressure to the wafer through the polish surface 112 and isoperable to rotate the polish head around a rotation axis 116. Therotation axis 116 is parallel with the rotation axis 106 and passesthrough the center of the polish surface 112. Thus, the polish surface112 is able to be pressed on the backside surface 104B of the wafer 104and to rotate relative to the wafer 104.

In some embodiments, the polish module 110 also includes a rinsing unit118 configured to rinse the backside surface of the wafer 104 with asolution or a chemical. In the present embodiments, the rinsing unit 118is movable for efficient cleaning effect or support the polishingprocess. For example, the rinsing unit 118 is movable from the center tothe edges of the wafer or from the edges to the center. The rinsing unit118 includes a rinsing tip 118A pointing at the backside surface 104Aand coupled to a source (not shown) that supplies rinsing chemical orsolution. The rinsing unit 118 and the polish head 110 are operable tosynergistically work together during a polishing process.

The polish module 100 includes an air bearing unit 120 designed toprovide an air pressure to the front surface 104A of the wafer 104. Theair bearing unit 120 provides an air pressure to the front surface 104Aof the wafer 104 so that the wafer 104 is maintained with the backsidepressure from the polish head 110 and the front pressure from the airbearing unit 120. The air bearing unit 120 provides an advantages thatinclude no direct contact and friction force between the bearing surfaceand the front surface 104A of the wafer. Especially, considering thatthe front surface 104A has circuit patterns and the wafer 104 spinsduring the polishing process, any damage to the circuit patterns on thefront surface 104A is eliminated.

The air bearing unit 120 is an aerostatic bearing. The air bearing unit120 is connected to a gas source 122, such as nitrogen source. In thepresent embodiment, the gas source 122 is a compressed nitrogen sourcethat delivers nitrogen with a pressure higher than the atmosphericpressure. The air bearing unit 120 includes a bearing surface 124 todeliver the gas to a bearing gap between the bearing surface 124 and thefront surface 104A of the wafer 104, thereby forming a fluid filmbetween the bearing surface 124 and the front surface 104A as an aircushion. The air bearing unit 120 further includes a gas path 126 thatconnects the gas source 122 and the bearing surface 124 for gasdelivery. In some embodiments, the bearing surface 124 includes a porousmaterial layer, such as a porous membrane or graphite, so that the gasis uniformly delivered to the bearing gap. In some embodiments, thebearing surface 124 includes a material layer with a plurality of micronozzles designed to uniformly deliver the gas to the bearing gap. Theair pressure in the bearing gap is able to be self-adjusted during thepolishing process. For example, when the gas pressure is higher, thebearing gap is increased, causing the gas flow rate being increased.Accordingly, the gas pressure is decreased through this self-adjustmentmechanism. In various examples, the air bearing unit 120 may includeother features, such as channels or groves on the bearing surface 124.

The air bearing unit 120 is integrated with the polish head 110. In thepresent embodiment, the air bearing unit 120 is mechanically connectedwith the polish head 110 so that the air bearing unit 120 is secured tothe polish head 110 and is able to move along with the polish head 110.This will be further described in details later.

The polish module 100 further includes an edge sealing unit 128 designedto seal the edges of wafer 104 such that chemical or solution from thebackside surface 104B of the wafer 104 cannot reach the front surface104A, therefor eliminating the contaminating to the front surface 104A.In some embodiments, the edge sealing unit 128 is an air sealing unit200 that is operable to form an air curtain around the edges of thewafer 104 for effective sealing. In some examples, the air sealingmechanism 200 includes a plurality of air nozzles configured in a ringto form a ring air curtain aligned with the edges of the wafer 104. Insome embodiments, as illustrated in FIG. 2 in a schematic view, the airsealing mechanism 200 includes a ring pipe 202 with a plurality ofopenings 204. The ring pipe 202 matches the edges of the wafer 104. Thering pipe 202 is also connected to a gas source 206 for delivering apressured gas, such as nitrogen. The openings 204 are formed on the ringpipe 200 with a configuration to generate an air curtain thateffectively protects the front surface 104A of the wafer 104 fromcontamination by the chemical or solution used to polish or clean thebackside surface 104B. In some other embodiments, the edge sealing unit128 is an O-ring sealing unit 300. The O-ring sealing unit 300 includesan O-ring 302 with a vertically extended edge curtain 304 to prevent thechemical or solution from contaminating the front surface 104A of thewafer 104, as illustrated in FIG. 3 in a schematic view.

The edge sealing unit 128 is integrated with a component (such as waferstage) of the polish module 100 or a fixture such that the edge sealingunit 128 is secured and is able to effectively seal the edge of wafer104 without interfering the motions of wafer 104 during variousoperations. This will be further described in details later.

FIG. 4 is a schematic and sectional view of the polish module 100 inportion, in accordance with some embodiments. By utilizing the airbearing unit 120, a fluid film 400, such as nitrogen film, is formedbetween the front surface 104A of the wafer 104 and the bearing surface124 of the air bearing unit 120. There is no direct contact between theair bearing unit 120 and the front surface 104A of the wafer 104 duringa polishing process. Therefore, the damage to the front surface 104A iseliminated. Furthermore, by utilizing the edge sealing unit 128, theedge sealing feature 402 is formed to effectively prevent the frontsurface 104A from contamination by the chemical or solution from thebackside surface 104B. In the present embodiment, the edge sealingfeature 402 is an air edge sealing feature, such as nitrogen knife toeffectively defend the front surface 104A. In some embodiments, the edgesealing feature 42 is an O-ring structure, such as the one illustratedin FIG. 3. The air bearing unit 120 and the edge sealing unit 128collectively protect the front surface 104A of the wafer 104 during apolishing process. Additionally, since the front surface 104A is notcontaminated during the polishing process, various cleaning measures forthe front surface 104A may be eliminated. Accordingly, the manufacturingcost is decreased and the manufacturing throughput is increased.

The polish module 100 is described above with reference to FIG. 1 andother figures. The polish module 100 may have other modifications,alternatives or a combination thereof. FIG. 5A illustrates a polishmodule 100 in a schematic and sectional view in accordance with someembodiments. The polish module 100 in FIG. 5A may be similar to thepolish module 100 in FIG. 1 in some aspects and may be different inother aspects. For examples, the polish head 110 may have a differentdesign, such as a smaller size. In some examples, the polish head 110has a polish surface 112 with a diameter less than the radius Rw of thewafer 104. In this case, the polishing head 110 further includes asweeping mechanism so that the polish head 110 is operable to moveradially along the sweeping direction 452. The sweeping direction 452 isin the radial direction of the wafer 104 from the wafer center (axis106) to the wafer edge. In one example, the mechanism 114 is designed tohave both rotation function and sweeping function. During a polishingprocess, the polish head 110 rotates around the axis 116 and movesradially along the sweep direction 452. Additionally, the wafer rotatesaround the axis 106 during the polishing process. By the combination ofwafer rotation, polish head rotation and polish head sweeping, thepolish surface 112 is able to sweep radially across the wafer and coverthe whole backside surface 104B of the wafer 104 during the polishingprocess. Especially, by adjusting the sweep dwell time, the polishingamount can be changed. Furthermore, the sweep dwell time can be variedlocally according to the locations from the center to the edge of thewafer. Thus, the polishing variation from the center to the edge can becompensated to achieve a uniform polishing surface by adjusting thesweep dwell time.

FIG. 5B illustrates a polish module 100 in a schematic and sectionalview in accordance with some embodiments. The polish module 100 in FIG.5B may be similar to the polish module 100 in FIG. 1 in some aspects andmay be different in other aspects. For examples, the substrate stage 102may have different design or using a suitable mechanism, such asclamping mechanism. In some examples, a gas valve 500 is configuredbetween the gas source 122 and the air bearing unit 120 to control thepressure of the air bearing for optimized bearing effect. The pressureof the air bearing may be further self-adjusted through the bearing gap,as noted above. In some examples, the edge sealing unit 128 is an airedge sealing unit contacted to a gas supply 502, such as a nitrogensource to provide a compressed and high pressure nitrogen gas. In someexamples, a second gas valve 504 is configured between the gas supply502 and the edge sealing unit 128 to control the gas flow. In someexamples, the edge sealing unit 128 may be connected to the gas source122 through a gas transportation mechanism 506 and shares the same gassource with the air bearing unit 120. In some embodiments, the polishsurface 112 may have different design. For examples, the polish surface112 may include a tape with abrasive particles attached to the tape. Theabrasive particles may have suitable size or size distribution fordesired polishing effect and may include diamond or other suitablematerials. In some examples, the polish surface 112 may include multiplerolls of abrasive tapes 508 configured for uniform and effectivepolishing.

In the present embodiment, the polish module 100 further includes apencil cleaning unit. The pencil cleaning unit and polish head 110 areoperable to be placed on the backside surface 104B of the wafer forrespective processes and be placed at an idle location. For example,when the polish head 110 is placed on the backside surface 104B of thewafer 104, the pencil cleaning unit is placed on the idle position. Whenthe pencil cleaning unit is placed on the backside surface 104B of thewafer 104, the polish head 110 is replaced at the idle location. FIG. 6is a schematic and sectional view of the polish module 100 in portion,in accordance with some embodiments. FIG. 6 illustrates the pencilcleaning unit 600 in the polish module 100 while the polish head 110 isnot shown in FIG. 6 for simplicity. The pencil cleaning unit 600 isdesigned to clean the polished surface of the wafer 104 after thepolishing process. In the present embodiment, the polished surface isthe backside surface 104B of the wafer 104. The pencil cleaning unit 600includes a sponge-like tip 602 that operable to clean the backsidesurface 104B of the wafer 104. The pencil cleaning unit 600 alsoincludes a mechanism, such as a movable arm 604, that is connected tothe sponge-like tip 602 and is able to control and manipulate thesponge-like tip 602 for cleaning. For example, the movable arm 604 cancontrol the sponge-like tip 602 to move radially along the direction 606from the center to the edges of the wafer 104 (or alternatively from theedges to the center) while the wafer 104 rotates around the axis 106 bythe substrate stage 102. Thus, the sponge-like tip 602 is able to cleanthe backside surface 104B. In some embodiments, the cleaning process iscollectively implemented by utilizing both the pencil cleaning unit 600and the rinsing unit 118.

As noted above, the air bearing unit 120 and the edge sealing unit 128are integrated with other components of the polish module 100 forsecuring and proper operations. The design and configuration furtherdepend on a particular structure used for the edge sealing unit 128,such as the O-ring edge sealing unit 300 or the air edge sealing unit200, further illustrated in FIGS. 7A and 7B, respectively.

FIG. 7A illustrates a schematic and sectional view of the polish module100, in portion, in accordance with some embodiments. In FIG. 7A, thepolish module 100 includes an O-ring edge sealing unit 300 that utilizesan O-ring structure 302 and an edge curtain 304 extended from the O-ringto seal the front surface of the wafer 104. In some embodiments, theO-ring structure 302 is operable to approach, or further attach to thefront surface 104A of wafer 104 for effective sealing. In this case, theO-ring edge sealing unit 300 (including the O-ring structure 302 and theedge curtain 304) is designed to be properly secured and to rotate alongwith the wafer 104 during various operations, such as polishing andcleaning. Particularly, the O-ring structure 302 and the edge curtain304 are connected to a stationary fixture 702 through a rotation bearingconnector 704. The stationary fixture 702 is a fixed component of thepolish module 100 and is stationary during various operations. Thus, theO-ring edge sealing unit 300 is secured to the stationary fixture 702and is still able to more along with the wafer 104. The wafer 104 issecured to the substrate stage 102 (such as by a wafer clamp structure)and moves along with the substrate stage 102.

Still referring to FIG. 7A, the air bearing unit 120 is integrated withthe polish head 110 and is secured to the polish head 110. Therefore,the air bearing unit 120 is able to move with and to be aligned with thepolish head 110 in order to provide a balance air pressure to the wafer104 from the front surface 104A. For example, when the polish head 110sweeps radially between the center and the edge of wafer 104, the airbearing unit 120 also moves radially with the polish head 110.Particularly, the air bearing unit 120 is integrated with the polishhead 110 through a frame connector 706 that is connected to both thepolish head 110 and the air bearing unit 120. The stationary fixture 702is designed to have an opening 708 so that the frame connector 706 isattached to the air bearing unit 120 through the opening 708 and is ableto move without interfering with the stationary fixture 702. In someembodiments, the polish module 100 further includes a linear bearingunit 710 configured between the stationary fixture 702 and the frameconnector 706 so that the frame connector 706 is able to move freelyrelative to the stationary fixture 702.

FIG. 7B illustrates a schematic and sectional view of the polish module100, in portion, in accordance with some embodiments. In FIG. 7B, thepolish module 100 includes an air edge sealing unit 200 that utilizesair sealing to the edge of wafer 104 so that the front surface 104A ofthee wafer is not contaminated by chemicals during polishing andcleaning operations. In the present embodiment, the air edge sealingunit 200 is secured on and fixed to the stationary fixture 702 so thatthe air edge sealing unit 200 is not movable when the wafer 104 rotatesduring the polishing and cleaning operations.

Still referring to FIG. 7B, the air bearing unit 120 is integrated withthe polish head 110 and is secured to the polish head 110, similar tothe integration structure of the air bearing unit 120 and the polishhead 110 in FIG. 7A. For example, the stationary fixture 702 is designedto have an opening 708 so that the frame connector 706 is attached tothe air bearing unit 120 through the opening 708 and is able to movewithout interfering with the stationary fixture 702. In another example,the polish module 100 further includes a linear bearing unit 710configured between the stationary fixture 702 and the frame connector706 so that the frame connector 706 is able to move freely relative tothe stationary fixture 702. In some examples, each of the stationaryfixture 702 and the frame connector 706 may include a suitable material,such as stainless steel, metal or metal alloy. In some examples, each ofthe stationary fixture 702 and the frame connector 706 may be made by aproper method, such as molding or machining.

FIG. 8 is a block diagram of a polish system 800 in accordance with someembodiments. The polish system 800 is a cluster tool having one or morepolish module 100 integrated in a processing chamber 802. In variousembodiments, the polish system 800 includes a plurality of polishmodules 100, such as 4, 6 or 8, properly configured and integrated. Inthe present example, 4 exemplary polish modules 100 are integratedtogether, as illustrated in FIG. 8.

The polish system 800 includes a load lock module 804 with one or moreload lock units for loading wafers to or unloading the wafers from thepolish system 800. In the present embodiments, the wafers are loaded andunloaded in batches, by using wafer containers, such as front openingunified pods (FOUPs).

The polish system 800 includes one or more robot 806 for handlingwafers. The robot 806 is configured between the load lock module 804 andthe processing chamber 802 in a way for proper wafer transferringbetween the polish modules 100 and the load lock module 804. Forexample, each wafer is transferred by the robot 806 from the load lockmodule to one of the polish modules 100 for a polishing process andthereafter is transferred back to the load lock unit module 804 by therobot 806. Since the disclosed polish system 800 is able to polish thebackside surface with simplified procedure, each polish module 100 canpolish, clean and dry the backside surface 104 of the wafer. Since thefront surface 104A of the wafer 104 is protected by the air bearing unit120 and the edge sealing unit 128, the cleaning and drying of the frontsurface 104A of the wafer 104 is eliminated. Thus the wafer 104 can beeffectively polished, cleaned and dried by one of the polish module 100,the plurality of polish modules 100 work in parallel for polishing,cleaning and drying multiple wafers simultaneously. The polish system800 may include other components, such as the chemical supply to therinsing units 118 of the polish module 100. The polish system 800 may beconfigured differently. For example, the air bearing units 120 of thepolish module 100 may share a same nitrogen source.

FIG. 9 is a flowchart of a method 900 for polishing one or moresemiconductor wafers 104, in accordance with some embodiments. Themethod 900 is implemented in the polish system 800 of FIG. 8. The method900 is described with reference to FIGS. 8, 9 and other figures.

The method 900 includes an operation 902 to load one or more wafers tothe polish system 800 through the load lock module 804. For example,wafers are in one or more batches, such as in FOUPs, are loaded to thepolish system 800 by the load lock module 804.

The method 900 includes operation 904 to transfer a wafer from the loadlock module 804 to one of the polish module 100 by the robot 806. Forexample, the robot 806 sequentially transfers 4 wafers to 4 polishmodules 100, respectively. In other example, the polish system 800 mayinclude two or more robots 806 to simultaneously transfer wafers torespective polish modules 100. Specifically, in the present embodiment,the wafer 104 is transferred to the substrate stage 102 of thecorresponding polish module 100 in a configuration that the frontsurface 104A faces the air bearing unit 120, as illustrated in FIG. 1.

The method 900 proceeds to an operation 906 to perform a polishingprocess to the wafer 104 in one of the polish modules 100. The operation906 and the following operations are described with one polish moduleand one wafer. However, as described above, the multiple wafers (such as4 wafers) may be processed in multiple polish modules in parallel. Inthe present embodiment, the backside surface 104B of the wafer 104 ispolished by the polish head 110 during the operation 906.

During the polishing process, various modules and units of the polishsystem 800 work collectively and synergistically. Accordingly, theoperation 906 includes various sub-operations. Especially, the operation906 includes a sub-operation 906A to polish the backside surface 104B ofthe wafer 104 by the polish head 110; an sub-operation 906B to providean air pressure to the front surface 104A of the wafer 104 by the airbearing unit 120; and a sub-operation 906C to seal the edges of wafer104 by the edge sealing unit 128.

The sub-operation 906A to polish the backside surface 104B of the wafer104 may include various polish modes. In some embodiments, thesub-operation 906A includes simultaneously rotating the wafer 104 aroundthe axis 106 and rotating the polish head 110 around the axis 116. Insome other embodiments, the polish head 110 has a small size, such asone illustrated in FIG. 5A. In this case, the sub-operation 906Aincludes simultaneously rotating the wafer 104 around the axis 106,rotating the polish head 110 around the axis 116, and sweeping thepolish head 110 radially.

The operation 906 may further include other sub-operations. In thepresent embodiments of the operation 906, the substrate stage 102secures the wafer 104 and rotates the wafer around the axis 106 with afirst rotation rate; the polish head 110 is placed and pressed onto thebackside surface 104B of the wafer 104 and rotates around the axis 116;the rinsing unit 118 may be applied to provide a rinsing solution to thebackside surface 104B of the wafer; the air bearing unit 120 providesthe air bearing to the front surface 104A of the wafer; and the edgesealing unit 128 provides edge sealing to the edges of the wafer 104. Insome embodiments, the first rotation rate ranges between 100 revolutionsper minute (RPM) and 180 RPM. Furthermore, the gas to the air bearingunit 120 may be adjusted through the first valve 500 and the gas to theedge sealing unit 128 may be adjusted through the second valve 504. Asan example for illustration, during the polishing process, the pressureto the backside surface 104B of the wafer 104 from the polish head 110may be tuned through the polishing process, such as a first pressureduring a first polishing phase and then a second pressure during asecond polishing phase. The second pressure is less than the firstpressure.

The method 900 proceeds to an operation 908 to perform a cleaningprocess to the backside surface 104B of the wafer 104 in the same polishmodule 100. In the present embodiment, the polish head 110 is replacedto an idle location and the pencil cleaning unit 600 is placed on thebackside surface 104B of the wafer 104. During the cleaning process,various modules and units of the polish system 800 work collectively andsynergistically. Especially, the substrate stage 102 secures the wafer104 and rotates the wafer around the axis 106 with a second rotationrate; the pencil cleaning unit 600 is placed and applied onto thebackside surface 104B of the wafer 104 and may move radially on thewafer 104; the rinsing unit 118 may be applied to provide a rinsingsolution to the backside surface 104B of the wafer 104; the air bearingunit 120 provides the air bearing to the front surface 104A of thewafer; and the edge sealing unit 128 provides edge sealing to the edgesof the wafer 104. In some embodiments, the second rotation rate isdifferent from the first rotation rate, such as less than the firstrotation rate. For examples, the second rotation rate may range between50 RPM and 150 RPM. Furthermore, the gas to the air bearing unit 120 maybe adjusted through the first valve 500 to a lower level thatcorresponds to the pressure from the sponge-like tip 602 of the pencilcleaning unit 600. In some examples, the rinsing unit 118 may deliver adifferent chemical solution for effective cleaning. In some examples forillustration, during the cleaning process, the sponge-like tip 602 ofthe pencil cleaning unit 600 may move from the center to the edges ofthe wafer 104.

The method 900 proceeds to an operation 910 to perform a drying processto the backside surface 104B of the wafer 104 in the same polish module100. In the present embodiment, the drying process is a spin-dryingprocess. The pencil cleaning unit 600 may be moved to an idle location.During the cleaning process, various modules and units of the polishsystem 800 work collectively and synergistically. Especially, thesubstrate stage 102 secures the wafer 104 and rotates the wafer aroundthe axis 106 with a third rotation rate substantially greater than thefirst and second rotation rates; and the edge sealing unit 128 providesedge sealing to the edges of the wafer 104. In some examples, the airbearing unit 120 may provide the air bearing to the front surface 104Aof the wafer. In some embodiments, the third rotation rate may rangebetween 500 RPM and 1500 RPM.

Thus, the backside surface 104B of the wafer 104 is polished, cleanedand dried in the same polish module. The front surface 104A of the waferis protected from the damage and contamination by the air bearing unit120 and the edge sealing unit 128. Various cleaning and drying processesto the front surface 104A are eliminated.

After the wafer 104 has been polished, cleaned and dried, the method 900includes an operation 912 to transfer the wafer 104 to the load lockmodule 804 by the robot 806. This operation is similar to the operation904 but it is reversed. For example, the multiple wafers are transferredto the load lock module 804 from the polish modules 100, respectively.

The method 900 may further include an operation 914 to unload the wafersfrom the polish system 800 through the load lock module 804. The method900 may include other operations, before, during or after the operationsdescribed above. For example, after the operation 912, the wafers may betransferred for lithography patterning process, such as photoresistcoating and exposure. Since the flatness of the backside surface of awafer is increased in addition to the enhanced flatness of the frontsurface of the wafer, the exposure process has improved quality.

The polish system 800 and the method 900 may further include otherembodiments, or alternatives. For examples, even though the method 800describes a procedure to polish the backside surface of a wafer forbackside surface flatness, the polish system and the method utilizingthe same may be used to polish the front surface of a wafer. In someembodiments, the method 900 may be used to thin down a wafer from thebackside surface, for the applications, such as 3D packaging ormicro-electromechanical systems (MEMS) packaging.

The present disclosure provides a polish system and a method utilizingthe same. By utilizing the disclosed polish system, the backside surfaceof the wafer is polished, cleaned and dried in a same polish module. Thefront surface of the wafer is protected from the damage andcontamination by the air bearing unit and the edge sealing unit.

The embodiments of the present disclosure offer advantages over existingart, though it is understood that other embodiments may offer differentadvantages, not all advantages are necessarily discussed herein, andthat no particular advantage is required for all embodiments. Variousadvantages may present in some embodiments. By utilizing the disclosedpolish system and the method, the front surface of the wafer isprotected from the damage and contamination by the air bearing unit andthe edge sealing unit. Various cleaning and drying processes to thefront surface are eliminated. The manufacturing cost is reduced and themanufacturing throughput is increased.

Furthermore, the lithography process is benefited from the improvedflatness of the wafer backside surface. When the integrated circuitsprogress to advanced technology nodes with small feature sizes and whena semiconductor substrate includes 3D devices, such as fin field effecttransistors (FinFETs), both the front and backside surface profiles willimpact the lithography patterning process and degrade the imagingresolution. The disclosed polish system and the method improve waferbackside surface flatness and improve the qualities of the lithographypatterning processes.

Thus, the present disclosure provides a semiconductor fabricationapparatus in accordance with one embodiment. The apparatus includes awafer stage that is operable to secure and rotate a wafer; a polish headconfigured to polish a backside surface of the wafer; an air bearingmodule configured to apply an air pressure to a front surface of thewafer; and an edge sealing unit configured to seal edges of the wafer.

The present disclosure provides a semiconductor fabrication system inaccordance with some embodiments. The semiconductor fabrication systemincludes a load lock module to load and unload plurality of wafers; aplurality of polish modules; and a robot unit configured between theload lock and the plurality modules, wherein the robot unit is operableto transfer one of the wafers to one of the polish modules. Each of thepolish modules further includes a wafer stage that is operable to securea wafer and rotate the wafer; a polish head configured to polish abackside surface of the wafer; and an air bearing module that isoperable to provide an air pressure to a front surface of the wafer.

The present disclosure provides a semiconductor fabrication method inaccordance with some embodiments. The method includes polishing abackside surface of a wafer; applying an air pressure to a front surfaceof the wafer during the polishing of the backside surface of the wafer;and sealing edges of the wafer during the polishing of the backsidesurface of the wafer.

The foregoing has outlined features of several embodiments. Thoseskilled in the art should appreciate that they may readily use thepresent disclosure as a basis for designing or modifying other processesand structures for carrying out the same purposes and/or achieving thesame advantages of the embodiments introduced herein. Those skilled inthe art should also realize that such equivalent constructions do notdepart from the spirit and scope of the present disclosure, and thatthey may make various changes, substitutions and alterations hereinwithout departing from the spirit and scope of the present disclosure.

What is claimed is:
 1. A semiconductor fabrication apparatus,comprising: a wafer stage that is operable to secure and rotate a wafer;a polish head configured to polish a backside surface of the wafer; anair bearing module configured to apply an air pressure to a frontsurface of the wafer; and an edge sealing unit configured to seal edgesof the wafer.
 2. The semiconductor fabrication apparatus of claim 1,further comprising a stationary fixture designed to secure the edgesealing unit and having an opening; and a frame connector that connectsthe air bearing unit and the polish head together through the opening.3. The semiconductor fabrication apparatus of claim 2, wherein the edgesealing unit includes an O-ring edge sealing unit to seal the edge ofthe wafer; and the O-ring edge sealing unit is secured to the stationaryfixture through a rotation bearing unit configured such that the O-ringedge sealing unit is able to move with the wafer.
 4. The semiconductorfabrication apparatus of claim 2, wherein the edge sealing unit includesan air edge sealing unit fixed to the stationary fixture.
 5. Thesemiconductor fabrication apparatus of claim 1, wherein the air bearingmodule is connected to a nitrogen source to provide nitrogen bearing tothe front surface of the wafer.
 6. The semiconductor fabricationapparatus of claim 5, wherein the air bearing module further includes abearing surface designed to deliver the nitrogen to a bearing gapbetween the front surface of the wafer and the bearing surface.
 7. Thesemiconductor fabrication apparatus of claim 6, wherein the bearingsurface includes a porous membrane.
 8. The semiconductor fabricationapparatus of claim 1, wherein the polish head includes a mechanism torotate the polish head around a center of the polish head.
 9. Thesemiconductor fabrication apparatus of claim 8, wherein the polish headincludes an abrasive surface designed to polish the backside surface ofthe wafer.
 10. The semiconductor fabrication apparatus of claim 8,wherein the polish head includes a plurality of abrasive tape rollsconfigured to polish the backside surface of the wafer.
 11. Thesemiconductor fabrication apparatus of claim 1, further comprising arinsing unit that is operable to rinse the backside surface of thewafer.
 12. The semiconductor fabrication apparatus of claim 1, furthercomprising a pencil cleaning unit that includes a sponge-like tip and isoperable to clean the backside surface of the wafer.
 13. A semiconductorfabrication system, comprising: a load lock module to load and unload aplurality of wafers; a plurality of polish modules, each of the polishmodules includes a wafer stage that is operable to secure a wafer androtate the wafer; a polish head configured to polish a backside surfaceof the wafer; and an air bearing module that is operable to provide anair pressure to a front surface of the wafer; a robot unit configuredbetween the load lock module and the plurality modules, wherein therobot unit is operable to transfer one of the wafers to one of thepolish modules.
 14. The semiconductor fabrication system of claim 13,wherein the each of the polish modules further includes an edge sealingunit configured to seal edges of the wafer, wherein the edge sealingunit is one of an air sealing unit and an O-ring structure.
 15. Thesemiconductor fabrication apparatus of claim 13, wherein the each of thepolish modules further includes a stationary fixture designed to securethe edge sealing unit; and a frame connector connecting the air bearingunit and the polish head together through an opening of the frameconnector.
 16. The semiconductor fabrication system of claim 13, whereinthe polish head includes a plurality of abrasive tape rolls configuredto polish the backside surface of the wafer; and the each of the polishmodules further includes a pencil cleaning unit having a sponge tip,wherein the pencil cleaning unit is operable to clean the backsidesurface of the wafer.
 17. A method, comprising: polishing a backsidesurface of a wafer; applying an air pressure to a front surface of thewafer during the polishing of the backside surface of the wafer; andsealing edges of the wafer during the polishing of the backside surfaceof the wafer.
 18. The method of claim 17, wherein the sealing of theedges of the wafer includes applying nitrogen to air-seal the edges ofthe wafer or using an O-ring structure to seal the edges of the wafer.19. The method of claim 17, further comprising performing a pencilcleaning process to the backside surface of the wafer; and spin-dryingthe backside surface of the wafer, wherein the polishing of the backsidesurface of the wafer includes rotating the wafer at a first rotationrate greater than zero, the performing of the pencil cleaning process tothe backside surface of the wafer includes rotating the wafer at asecond rotation rate greater than zero, and the spin-drying of thebackside surface of the wafer includes rotating the wafer at a thirdrotation rate greater than the first and second rotation rates.
 20. Themethod of claim 19, wherein the polishing of the backside surface of thewafer further includes rotating a polish head and sweeping the polishhead radially simultaneously.